This proposal deals with the use of Electron Spin Resonance and spin-labelling and spin trapping techniques in the study of molecular carcinogenesis. Specific studies are aimed at the role of lipid peroxidation and free radical activation in carcinogenesis. Spin-labelling experiments have been designed to study the binding mechanism of carcinogens to cellular constituents, particularly DNA and intact chromatin. Additional spin-labelling experiments have been designed to probe the mechanism of DNA-Histone interaction and the structural functional relationships of the estrogen receptor protein from mammary tumor tissue.